Re: [PATCH 39/43] xfs: support write life time based data placement

Darrick J. Wong
2025-02-13T04:42:47Z

On Wed, Feb 12, 2025 at 01:29:21PM +0000, Hans Holmberg wrote:
> On 12/02/2025 01:27, Darrick J. Wong wrote:
> > On Thu, Feb 06, 2025 at 07:44:55AM +0100, Christoph Hellwig wrote:
> >> From: Hans Holmberg <hans.holmberg@wdc.com>
> >>
> >> Add a file write life time data placement allocation scheme that aims to
> >> minimize fragmentation and thereby to do two things:
> >>
> >> a) separate file data to different zones when possible.
> >> b) colocate file data of similar life times when feasible.
> >>
> >> To get best results, average file sizes should align with the zone
> >> capacity that is reported through the XFS_IOC_FSGEOMETRY ioctl.
> >>
> >> For RocksDB using leveled compaction, the lifetime hints can improve
> >> throughput for overwrite workloads at 80% file system utilization by
> >> ~10%.
> >
> > The code changes look mostly ok, but how does it do at 40% utilization?
> > 99%? Does it reduce the amount of relocation work that the gc must do?
>
> The improvement in data placement efficiency will always be there,
> reducing the number of blocks requiring relocation by GC, but the impact
> on performance varies depending on how full the file system is.
>
> At 40% utilization there is almost no garbage collection going on, so the
> impact on throughput is not significant. At 99% the effects of better
> data placement should be higher.

<nod> Would you mind pasting that into the commit message?

--D

> Cheers,
> Hans
>